1. Field of the Invention
The present invention relates to a distance measuring apparatus, and particularly to a distance measuring apparatus of, for example, a camera using a passive AF sensor.
2. Description of the Related Art
The distance measurement using a passive AF sensor is known as a process of imaging a distance measurement object by, for example, a pair of left and right line sensors and calculating the distance from the distance measurement object from the amount of deviation between left and right sensor images obtained by the left and right line sensors.
The deviation amount of sensor images can be determined by setting window ranges in left and right line sensors, respectively, determining the level of correlation of a pair of left and right sensor data showing sensor images in the window ranges with a pair of left and right window ranges being relatively shifted in left and right directions, and detecting a shift amount in the window ranges providing the highest correlation level.
Also, it is described in Japanese Patent Publication Nos. 3-48484 and 6-93059 that the distance from a distance measurement object can accurately be determined by determining the correlation level of data showing the contrast of sensor images instead of determining the correlation level of sensor data showing sensor images. Data showing the contrast of sensor images is, for example, difference data obtained by determining a difference (two-pixel difference) between sensor data and the data into which the sensor data is shifted by a predetermined number of pixels for sensor data of each line sensor. That is, the correlation level is determined according to difference data obtained by subtracting from sensor data of a cell watched when each of cells is watched the sensor data of the cell separated by a predetermined number of pixels from the watched cell.
Furthermore, data showing the contrast of sensor images is not difference data, but may be data showing the ratio between sensor data and the data into which the sensor data is shifted by a predetermined number of pixels for sensor data of each line sensor. Also, in this specification, data that is used for determining the correlation level is referred to as AF data.
In the case where data showing the contrast of sensor images is used as AF data, however, there are disadvantages that time is required for generating AF data from sensor data to prolong distance measurement time, and a special circuit is required for generating AF data from sensor data.